Production of paraffin fuels using renewable materials by a continuous hydrotreatment comprising a pre-treatment step under hydrogen

Abstract

A process for hydrotreatment of a feed from renewable sources such as vegetable oils for the production of paraffinic hydrocarbons comprising a pre-treatment step by crystallization and/or precipitation and pre-hydrogenation of the feed under hydrogen allowing the elimination of insoluble inorganic impurities under hydrotreatment conditions and improved exothermal management of the reaction. The effluent is separated to a gas fraction and a liquid fraction containing paraffinic hydrocarbons, a portion of said liquid fraction is recycled.

The invention claimed is: 
     
       1. A process for the hydrotreatment of a feed originating from renewable sources in order to produce paraffinic hydrocarbons, comprising at least:
 a) mixing a total feed flow F0 with a recycle flow RPP comprising at least a portion of a liquid fraction R containing paraffinic hydrocarbons from separation d) and with a flow of a hydrogen-rich gas H 2 P, to produce a mixture M, bringing mixture M to a temperature of between 140 and 250° C.; 
 b) preheating said mixture M in a pre-treatment zone in which flow of said mixture M takes place via a porous medium consisting of a particle bed referred to as a fixed bed, said particle bed comprising solid catalytic materials that are optionally mixed with solid non-catalytic materials and said fixed bed having a void fraction of between 0.25 and 0.8; 
 c) hydrotreating at least one effluent resulting from pre-treatment in b) (F+εRPP+δH 2 PP), ε and δ being between 0 and 1, in the presence of hydrogen in excess of theoretical hydrogen consumption and under hydrotreatment conditions in a fixed bed reactor having a plurality of catalytic zones disposed in series and comprising a hydrotreatment catalyst, dividing said effluent into at least a certain number of different part flows (F1+ε 1 RPP+δ 1 H 2 PP) to (Fn+ε n RPP+δ n H 2 PP) equal to the number of catalytic zones n in the reactor, injecting a first part flow (F1+ε 1 RPP+δ 1 H 2 PP) into a first catalytic zone, a second part flow (F2+ε 2 RPP+δ 2 H 2 PP) is injected into a second catalytic zone and so on, if n greater than 2; injecting various part flows into successive catalytic zones in increasing proportions such that F1/F is less than or equal to F2/F, which itself is less than or equal to F3/F and so on until F(n−1)/F is less than or equal to Fn/F, in order to produce an effluent containing paraffinic hydrocarbons; 
 d) separating said effluent containing paraffinic hydrocarbons in at least one separation allowing separation of at least one gaseous fraction and at least one liquid fraction containing the paraffinic hydrocarbons; 
 e) dividing at least a portion R of said liquid fraction containing the paraffinic hydrocarbons from b) into at least a flow RLC and into said recycle flow RPP upstream of a) and mixed with the total feed flow F0 and said flow RLC is divided into at least a certain number of different part flows R1-Rn less than or equal to the number of catalytic zones n in the reactor, said flows R1-Rn being recycled upstream of the catalytic zones 1-n, so that the weight ratio between the flow of paraffinic hydrocarbons (R1+δ 1 RPP) sent to the first catalytic zone and the part flow F1 of the feed introduced into the first catalytic zone is greater than or equal to 10. 
 
     
     
       2. The process according to  claim 1  in which said feed originating from renewable sources contains triglycerides and/or free fatty acids and/or esters and is an oil or fat of vegetable or animal origin or a mixture of such feeds. 
     
     
       3. The process according to  claim 1  in which the proportion of the flow RPP introduced in a) in relation to the flow of total fresh feed F0 is such that the mass flow ratio RPP/F0 is between 0.1 and 5. 
     
     
       4. The process according to  claim 3  in which the mass flow ratio RPP/F0 is between 0.5 and 3. 
     
     
       5. The process according to  claim 1  in which said hydrogen-rich gas flow H2P comprises at least a part of the gaseous fraction from separation d) having undergone a purification step, optionally in a mixture with fresh hydrogen. 
     
     
       6. The process according to  claim 1  in which the flow H 2 P introduced in a) in relation to the total fresh feed flow F0 is in an amount whereby the standard volumetric delivery of the hydrogen-rich flow to the volumetric delivery of the fresh feed H 2 P/F0 is in a ratio between 100 and 1500 NL/L. 
     
     
       7. The process according to  claim 1  in which the catalytic solid materials used in pre-treatment b) are catalysts comprising one or more elements from groups 6, 8, 9 or 10 of the periodic table and a support of alumina, silica, silica-alumina, magnesia, clay, a ‘Kieselguhr’ support or a mixture thereof. 
     
     
       8. The process according to  claim 1  in which said non-catalytic solid materials used in pre-treatment b) are porous refractory oxides that are alumina, silica, activated alumina, silica-alumina, a metal oxide, non-metal oxides, oxide ceramic, non-oxide ceramic, or composite ceramic, silicon carbide, activated carbon, calcium aluminate, metal, graphite, clay or magnesia. 
     
     
       9. The process according to  claim 1  in which said pre-treatment d) comprises in addition to the pre-treatment zone, a separation zone. 
     
     
       10. The process according to  claim 9  in which effluent from the pre-treatment zone is introduced into a separation zone in order to separate at least one effluent to be hydrotreated, containing triglycerides (F+εRPP+δ H 2 PP) with ε and δ of between 0 and 1, at least one paraffin-rich liquid effluent ((1-ε) RPP+αH 2 PP) and at least one hydrogen-rich gaseous effluent (1-δ-α)H 2 P with (α+δ) of between 0 and 1. 
     
     
       11. The process according to  claim 1  having a total recycle rate (RT) less than 1.0. 
     
     
       12. The process according to  claim 1  wherein mass flow RPP/R ratio is between 0.1 and 0.9. 
     
     
       13. The process according to  claim 1  in which said feed from renewable sources is treated in a mixture with gas oils, kerosenes or gasolines from oil refining processes. 
     
     
       14. The process according to  claim 1  in which at least a portion of the liquid fraction containing the paraffinic hydrocarbons from separation d) not recycled is hydroisomerized in the presence of a hydroisomerization catalyst.